I am going to buy the head of one of these razors to use with a stainless steel handle I already have. Has anyone used both of these razors? If so, can you compare the two>? which razor gives you a smoother shave? please help if you can. I heard the tech is pretty aggressive. I wonder how the shavecraft short comb compares to it.

The Tech is very aggressive and similar to the Muhle R41, but a bit smoother, whereas the Short-Comb is a milder shaver. I would suggest the latter if you want a more enjoyable and relaxed shave. However, if you prefer your razor on the very aggressive side, then go with the Tech.
You could always try to get one top-plate and both of these bottom-plates to decide which one suits you.
Good luck.